Direction finder



A g- 1939- P. HERMANSPANN 2,170,360

DIRECTION FINDER Filed Aug. 21, 1936 Fig.1 v [4 .2

'INVENTOR PAUL HERMANSPANN ATTORNEY Patented Aug. 29, 1939 DIRECTION FINDER tion of Germany Application August 21, 1936, Serial No. 97,090 In Germany August 29, 1935 2 Claims.

This invention relates to a direction finder circuit arrangement and is more particularly adapted to receivers.

A great many methods have been proposed for 5 carrying out a destination flight through taking bearing of a transmitter for destination flight. One of these methods resides in the fact that the combination of a frame antenna and an auxiliary antenna serve for determining the direction.

Referring to the accompanying drawing Figure 1 illustrates characteristic directive curves of a pair of antennae illustrated in Figure 2, while Figure 3 illustrates a circuit for enabling the coupling between the two antennas of Figure 2 to be periodically reversed and includes an embodiment of my invention.

Through the coaction of frame R in Fig. 2 and auxiliary antenna A, directive characteristics are produced such as rep-resented by the curves m and Ch2 in Fig. 1, whereby the different directive actions are due to the mutual coupling of the two antennas taking place in the one sense and then in the opposite sense. For the destination flight, this condition is utilized in such manner that the coupling is being reversed in rapid succession by means of a switch for instance in the rhythm of complementary Morse signals, so that the two characteristics Ch]. and C112 of Fig. 1 appear in succession. In a head piece connected to the receiver, the two Morse signals form together a steady note only when the transmitter lies in the direction indicated by the arrow OZ. Thus, if frame and auxiliary antennas are fixedly mounted on the airplane, the proper direction of flight will be indicated by the steady note.

An example of such station is shown in Fig. 3.

The antenna l is tuned to the operating Wave of the transmitter by the inductance 2, and by the capacitance 3. The same is true for the frame antenna I0 with the circuit elements 8 and 9. The coupling of both antennas takes place across coil 1 and the switching means 4, 5, 6 in such a manner that for instance the directional diagram Chi will be obtained when the switch lever 4 is 45 placed at contact 5, while the diagram Chz will be produced when 4 is at 6. The high-frequency current arriving from the antenna I thus passes in the one case through the upper part of coil 1, and when the switch is in the other position, it passes through the lower part, so that the voltages or currents arriving from the frame and from the auxiliary antenna appear according to the position of the switch either in equal phase or in opposite phase in the receiver which may be 55 coupled to the coil 8.

In the operation of such station, the difiiculty is encountered that despite the proper direction of flight, i.e. when the transmitter lies in the direction 2., no pure steady note is obtained, but the note is disturbed by more or less strong cracking noises so that an exact observation of the direction of flight becomes impossible.

It was found that the described cracking noises are caused by charging phenomena at the switch lever 4.

In accordance with the invention, the cracking noises are avoided or at least reduced in that the switch lever is connected to ground through a resistance II.

The center tap of coil 1 is placed at ground, while the ends thereof are connected to the switch contacts and 6.

The idea of the invention is not limited to the example of construction shown, and the latter may also be formed in any other desired way. It is particularly suited, also, for all other receiver arrangements in which antenna circuits or other high-frequency circuits are interrupted or varied by means of a switch at the switched-in receiver.

What is claimed is:

1. In a system as described a center-tapped coupling coil having its center tap grounded and switch contacts connected to each end of said coil, a switch arm adapted to alternately engage each of said contacts whereby the coupling sense of said coil may be reversed, a tuning coil having an end connected to said switch arm, the other end of said tuning coil connected to one side of a condenser, the other side of said condenser being grounded and a resistance connected between said switch arm and ground whereby the tuned circuit formed by said tuning coil and condenser is at no time broken.

2. A direction finder system comprising a loop antenna and an auxiliary antenna, a tuned circuit connected to said loop, a tuned circuitcomprising a coil and a condenser, each having one terminal connected to said auxiliary antenna, said condenser having one terminal connected to ground, a switch arm connected to the other terminal of said coil, means for coupling said tuned circuits including a center tapped coil coupled to the said loop tuned circuit and having its center tap grounded, switch contacts conneoted to each end of said coil and associated With said switch arm whereby the coupling between said antennas may be periodically reversed and a resistor having one end connected to said switch arm and the other end grounded whereby said second mentioned tuned circuit is at all times continuous to reduce noise caused by actuation of said switch.

PAUL HERMANSPANN. 

